It is generally known that containers for storing carbonated beverages necessitate an overpressure relief system. Such an overpressure relief system has the aim to prevent uncontrolled burst of the container or closure or an uncontrolled ejection of a valve or closure fixed thereto. Existing overpressure relief systems included containers having weakened spots in their body so as to allow a controlled burst in case of overpressure of the use of overpressure valves. With the increasing interest in home appliances, containers with weakened spots in their body have become undesirable, while valves are considered as expensive and as such also undesired. Accordingly, overpressure relief systems have been incorporated in the closure of containers.
Overpressure release systems are described in the art. For example EP-A-1 614 636 and U.S. Pat. No. 5,328,063 both disclose a closure comprising a mount piece that is snap fitted on a container and defining an outflow opening thereof. Centrally in the outflow opening is provided a stem that is an integral part of the mount piece. The closure further comprises a closure cap fixed to the mount piece, the closure cap comprising a flexible diaphragm sealing an outlet of the container and having a free edge that engages the stem. When overpressure occurs in the container, the flexible diaphragm deforms and an opening is created between the stem and the free end of the diaphragm, thereby allowing overpressure relief.
A drawback of the prior art closures incorporating an overpressure relief system is that the essentially comprise a flexible diaphragm, which clearly limits design options with respect to access control by example given piercing. Another drawback is that said closures comprise different materials, in particular a rigid portion for the fixation of the closure to the mount piece of container and a flexible portion for allowing overpressure relief. Hence, the manufacturing and recycling of the known closures is relatively complicated and expensive.